1. Field of the Invention
The present invention relates to a rewritable phase-change optical information recording medium having a large recording capacity and capable of rewriting information recorded therein.
2. Discussion of Background
As optical information recording media which are capable of recording information therein, and from which recorded information can be reproduced or erased by the application of semi-conductor laser beams thereto, there are conventionally known (1) a magneto-optical recording medium in which information can be recorded, and recorded information can be erased by reversing a magnetization direction of a recording layer thereof, utilizing heat, and (2) a phase-change optical information recording medium in which information can be recorded, and recorded information can be erased, utilizing phase changes between a crystalline phase and an amorphous phase of a recording layer thereof.
The latter phase-change optical information recording medium is capable of performing single beam overwriting, and is advantageous over other optical recording media in the compatibility with CD-ROM and CD-R media, so that the standardization of the phase-change optical information recording media as rewritable media, namely as CD-RW, has now been established, and the phase-change optical information media have now been commercialized.
In the meantime, large capacity storage by the phase-change optical information recording media has been studied, and DVD-ROM media have been placed on the market. In accordance with the appearance of the DVD-ROM on the market, media called DVD-RAM are now being developed as rewritable DVD media. A DVD-RAM with a capacity of 2.6 GB will be shortly commercialized, but there is now a demand for a DVD-RAM with a capacity larger than that of ROM media.
As the materials for use in the recording layer of the phase-change optical information recording medium, chalcogen-based alloys, such as Gexe2x80x94Sbxe2x80x94Te, Inxe2x80x94Sbxe2x80x94Te, Gexe2x80x94Sexe2x80x94Te, Gexe2x80x94Texe2x80x94Bi, Sbxe2x80x94Sexe2x80x94Te, and Inxe2x80x94Texe2x80x94Au have been investigated. Of these chalcogen-based alloys, Gexe2x80x94Sbxe2x80x94Te has now reached a level for use in practice. However, even with this Gexe2x80x94Sbxe2x80x94Te, further improvements are desired on the recording sensitivity, erasing sensitivity, and erasing ratio at overwriting.
Japanese Laid-Open Patent Applications 4-78031 and 9-263055 disclose phase-change information recording media using as recording materials in the recording layers thereof Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te based alloys by use of which the erasing ratio of the phase-change information recording media at the overwriting is improved.
However, the repeated use overwriting characteristics of a phase-change optical information recording medium using the above-mentioned Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te based recording material cannot be improved by using the Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te based recording materials only, but by using upper and lower protective layers, and a heat dissipation layer which are overlaid.
As the materials for such protective layers, ZnS.SiO2 as disclosed in Japanese Patent Publication 7-114031, metallic oxides, metallic sulfides and metallic nitrides, and mixtures thereof are conventionally proposed. However, the improvement of the repeated use overwriting characteristics of the phase-change optical information recording medium is still insufficient for use in practice.
As mentioned above, the phase-change optical information recording media have now been commercialized as CD-RW. The CD-RW is used as an external memory device for use with personal computers. Recently DVD-ROM players are placed on the market, so that there is a great demand for large capacity, rewritable DVD media.
The DVD-RAM which has now been commercialized as rewritable DVD medium has a capacity of 2.6 GB, and recording and reproduction is conducted at a linear speed of about 6 m/sec, while in DVD-ROM, the linear speed for recording and reproduction is about 3.5 m/sec, and the capacity of DVD-ROM is 4.7 GB. It is required that rewritable DVD media have a capacity greater than that of ROM, be capable of performing recording and reproduction at a speed of two times greater than that of ROM, and be compatible with ROM. In order to meet such requirements, it is strictly required that the DVD media have a high line density, a low jitter, and a large overwriting repetition number. In particular, the improvement of the overwriting repetition number is one of most significant targets to be cleared in the phase-change optical information recording media in order to enhance the performance reliability of the media. The Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te based phase-change recording materials are suitable for high density recording, so that how to improve the overwriting repetition characteristics thereof is still a significant target to be cleared.
It is therefore a first object of the present invention to provide an Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te based phase-change optical information recording medium with high overwriting repetition number, high recording density, excellent recording and reproduction characteristics capable of attaining high speed recording and reproduction.
A second object of the present invention to provide a heat dissipation layer and a protective layer for use in the above-mentioned optical information recording medium of the present invention in order to attain the above object of the present invention, in particular, high speed recording and reproduction.
The first and second objects of the present invention can be achieved by an optical information recording medium comprising:
a first dielectric protective layer,
a recording layer provided on said first dielectric protective layer, comprising a material represented by a chemical formula of Agxcex1Inxcex2Sbxcex3Texcex4, wherein xcex1, xcex2, xcex3 and xcex4 respectively represent an atomic percent of Ag, an atomic percent of In, an atomic percent of Sb, and an atomic percent of Te, and satisfy the conditions of:
1xe2x89xa6xcex1 less than 10,
1 less than xcex2xe2x89xa620,
35xe2x89xa6xcex3xe2x89xa670,
20xe2x89xa6xcex4xe2x89xa635,
xcex1+xcex2+xcex3+xcex4=100,
4xcex2xe2x88x92xcex4xe2x89xa60,
xcex3xe2x88x922xcex4xe2x89xa70, and
xcex3xe2x88x928xcex1xe2x89xa70,
a second dielectric protective layer provided on said recording layer, and
a light reflection and heat dissipation layer provided on said second dielectric protective layer.
The above-mentioned optical information recording medium may further comprise a heat dissipation layer which is interposed between the second dielectric protective layer and the light reflection and heat dissipation layer, the heat dissipation layer comprising a material which comprises Mg, In and O, with the atomic ratios of Mg and In satisfying a formula of 0.60 less than In /(In+Mg) less than 1.0.
Furthermore, in the above-mentioned optical information recording medium , it is preferable that the heat dissipation layer and the second dielectric protective layer respectively have a thickness of D1 and a thickness of D2, with a ratio of D1:D2 being in a range of (10:90) to (50:50).
It is also preferable that in the above-mentioned optical information recording medium, the heat dissipation layer have a refractive index of 1.9 to 2.1.